WASHINGTON (WUSA9) -- It's a rare peek into the eyes and movements of a killer.

The FBI released video and pictures today of Navy Yard gunman Aaron Alexis minutes before he opened fire, and we want to warn you, some may not like seeing this.

Know that our hearts go out to the friends and families of the victims of that shooting spree. It was a tough choice to make to show parts of this video but we think it's crucial to analyze Alexis' behavior so that you may be able to spot a sign before it turns into something possibly more sinister.

Experts can tell a lot from the cues a person gives, the way they walk, move their hands, their gaze, their pace. We asked body language expert Chris Ulrich to analyze the Navy Yard shooter's movements, "It's gut wrenching to watch it. When he walks in, what's going on with his body language, what's he doing in his face? Is he nervous, is he looking around quickly."

The video shows Alexis calmly entering Building 197. Ulrich says, "He's opening up the door, he's walking in, he's at a normal slow easy pace." But then, Ulrich says things change, "Now, as he comes through here, he'll open this door, and this is interesting, he comes down into this imploded body posture. On top of it, there's some fear involved, because he's pausing, he's looking around. It's a conflict within the attacker, the aggressor, back and forth, even the aggressor has some fear."

Them Ulrich points out the biggest clue, when Alexis seems to launch into attack mode, "The chin goes down, and usually when we see someone with their chin down, they're a step away from this point from lunging into action."

Was there anything anyone could have done to prevent this? We may never know.

But Ulrich's says in your everyday interactions, look closer, "We call it inattentive blindness, people who see information right before our eyes but we don't even see it. We're looking for anything that is out of the ordinary. How do they normally sit, how do they use their hands on a regular basis, what's their baseline? He says when you see anything that deviates from the norm, that's cause for attention.

Admittedly, the video can be tough to watch. Ulrich says it's also tough to ignore, "I think we need to see this to know from the reality that this is out there, that this is happening."